Exponential Performance Regression in Rust 1.73 Read API from BorrowedCursor::ensure_init #117545
Description
Reported by a lz4_flex user PSeitz/lz4_flex#147
Code
I created a small repo to demonstrate on a minimal example.
https://github.com/PSeitz/copy_regression_1.73
BorrowedCursor::ensure_init from this PR #97015 seems exhibit exponential cost.
The program creates a Vec and reads it in chunks of 32kb. Size is specified as a command line argument (100MB-400MB).
time cargo run --release 100000000 (If your default is 1.73)
Executed in 3.84 secs fish external usr time 3.80 secs 268.00 micros 3.80 secs sys time 0.03 secs 262.00 micros 0.03 secs time cargo run --release 200000000
Executed in 16.90 secs fish external usr time 16.82 secs 626.00 micros 16.82 secs sys time 0.04 secs 0.00 micros 0.04 secs time cargo run --release 400000000
Executed in 72.84 secs fish external usr time 72.65 secs 586.00 micros 72.65 secs sys time 0.06 secs 138.00 micros 0.06 secs time cargo +1.72 run --release 100000000
Executed in 57.23 millis fish external usr time 16.83 millis 404.00 micros 16.43 millis sys time 37.02 millis 0.00 micros 37.02 millis time cargo +1.72 run --release 400000000
Executed in 257.30 millis fish external usr time 150.46 millis 477.00 micros 149.98 millis sys time 106.64 millis 112.00 micros 106.53 millis